This invention relates to the dental cement composition, and in more detail, this invention relates to dental cement compositions which, in contrast to the conventional aqueous dental cement compositions, are practically non-aqueous, being excellent in initial adhesion, cementing, and filling ability to the tooth, and showing excellent strength and water-resistance after setting.
Among many kinds of dental cement now available to us, the most frequently used are the phosphate cement based on the reaction between zinc oxide and phosphoric acid, the polycarboxylate cement based on the reaction between zinc oxide and polycarboxylic acid, the zinc oxide-eugenol cement based on the reaction between zinc oxide and eugenol, and the glass-ionomer cement based on the reaction between fluoroaluminosilicate glass powder and polycarboxylic acid, among which the glass ionomer cement is frequently used as the most preferable cement.
Each of these dental cement has advantages and disadvantages, and none of them is ideal. For example, the zinc phosphate cement has poor adhesion to the tooth and shows irritability due to phosphoric acid at the beginning of setting; the polycarboxylate cement has poor final strength of the set cement; the eugenol cement is poor in the strength and in the intraoral durability, so that it is used only for temporary sealing or temporary cementing, and the irritability specific to eugenol is a disadvantage.
In contrast to these cement, the glass ionomer cement is excellent in biocompatibility, adhesion to the tooth, intraoral durability in the mouth, etc., and in addition, it is excellent from the esthetic viewpoint because it is translucent. Based on these characteristics, the glass ionomer cement is widely used for cementing of inlay, crown, etc., filling of caries cavities, lining, preventive filling of pits and fissures, etc.
The most undesirable characteristic of the glass ionomer cement is that the setting reaction is inhibited when the cement comes in contact with water such as saliva in the initial stage immediately after mixing, which may finally result in deteriorated physical properties. That is, although the glass ionomer cement begins to set in the presence of water based on the chelate formation between a polycarboxylic acid and a polyvalent metal derived from fluoroaluminosilicate glass, that is, the setting reaction requires water for release of metal ions, water present in the setting system or the setting cement is undesirable for increase of setting rate or of initial strength. In addition, when the setting reaction proceeds in the presence of water, the surface of the setting cement becomes white-clouded, which is undesirable from the esthetic viewpoint.
Various techniques to eliminate these disadvantages of the glass ionomer cement have been developed; for example, addition of an organic chelating agent to increase the initial setting rate (Japanese Patent Publication No.21858/1979), addition of a fluoro-complex to increase the initial setting rate (Japanese Unexamined Patent Publication No.2210/1982), combination of a polymerizable unsaturated compound and a polymerization catalyst to increase the initial setting rate (Japanese Patent Publication No.27049/1994), etc. have been proposed and seem to be effective in their own way.
However, usual dental cement including the above-mentioned glass ionomer cement are always used in the form of an aqueous paste for acceleration of the metal cross linking reaction between the polyvalent metal in the cement powder and a polycarboxylic acid. Therefore, as mentioned above, the presence of water exerts not a small undesirable influence on the setting rate and the initial strength, so that the quality-improving effect is smaller than expected.